1. Field of the Invention
The present invention relates to method and apparatus for positively feeding yarns of indefinite lengths from a yarn source to a knitting machine or the like.
2. Description of the Prior Art
In the present state of the knitting art, particularly when using multifeed circular knitting machines, it is highly desirable to interpose a positive feeding device between the yarn supply and the knitting stations of the machine, said positive feeding device drawing the yarn from the yarn supply and directing it to its respective knitting station at substantially the rate the knitting station consumes the yarn. In the absence of such a device, the consumption of the yarn at the knitting station would draw the yarn from the supply. The reasons why the use of positive feeding devices are desirable are well known in the art and need not be further discussed herein. Many positive feeding devices have been proposed and some are being used commercially, but such devices have various deficiencies.
One type of positive feeding device in relatively widespread commercial use is that generally described in Rosen U.S. Pat. Nos. 3,090,215 and 3,243,091, frequently called a Rosen type. This device has a plurality of circumferentially spaced apart idler rollers mounted above the knitting machine, said rollers being driven by a yarn feeding endless tape trained around the rollers, the tape being driven by the knitting machine drive. There is one roller for each knitting station and the yarn corresponding to that station is directed between the periphery of the corresponding roller and the contacting surface of the tape. Rotation of the tape causes the roller to rotate, the mating surfaces of the tape and roller frictionally engaging the yarn therebetween to draw the yarn from the supply and direct it toward the knitting station.
There are two principal shortcomings of the Rosen tape. The yarn frequently slips between the mating surfaces of the tape and roller, with the result that the yarn is not delivered at the desired rate. Furthermore, a Rosen type cannot provide different rates of feeding for different knitting stations. The rate of feeding depends upon the lineal speed of the mating surfaces of the tape and roller. The lineal speed of these mating surfaces is determined by the lineal speed of the tape and is independent of the diameter of the rollers. Since a plurality of rollers are driven by a single tape, all of the rollers must feed their respective yarns at the same rate, even if the rollers have different diameters. In order for some yarns to be delivered at a rate different from other yarns, it is necessary to have, for each rate of delivery, a separate Rosen tape with its own set of rollers. It is rare to have more than two or three Rosen tapes on a machine because of mechanical and space problems, as well as cost problems. It is impossible to independently select the feeding rate for each knitting station fed by that tape.
U.S. Pat. No. 3,361,317 to Levi discloses a positive feeding device which also utilizes a plurality of circumferentially spaced apart rollers driven by an endless belt trained about the rollers, the rollers having a projecting peripheral portion not contacted by the belt. The yarn being fed is directed around the projecting portion and is fed by the frictional engagement between the surface of the projecting portion and the yarn. Although the projecting portion may be covered with friction material to reduce yarn slippage, slippage does occur since the yarn is not positively gripped between opposed surfaces. The rate of delivery depends upon the lineal speed of the surface of the projecting roller portion. Therefore, by providing rollers whose projecting portions have different diameters, it is possible to obtain different rates of feeding for different knitting stations, although the patent has no such suggestion of simulataneously providing different feeding rates. In order to change the rate of delivery of a particular roller, it would have to be replaced by another roller and this is a cumbersome operation.
U.S. Pat. No. 2,708,841 to Lumsden discloses an apparatus for feeding elastic rubber yarns. The apparatus utilizes a plurality of driven pulleys comprising interlaced fingers, the fingers being at an angle to the plane of the pulley to provide a type of V-grooved pulley. Although these pulleys may be adequate for feeding rubber yarn because of the surface friction characteristics of the yarn, the fingers are so circumferentially spaced apart that ordinary yarns will slip. The pulleys are not adjustable for providing different rates of delivery.
It has also been suggested to provide positive feeding devices which comprise pairs of meshing gears of various shapes. The yarn passes between the opposed surfaces of the meshing gears and rotation of the gears causes the yarn to be fed. Such constructions not only permit slippage but the opposed surfaces of the gears can easily damage the yarn by crushing or tearing it.